• Why are fluorescent proteins  fluorescent?
  A general fundamental mechanism that applies to all fluorescent proteins has notbeen clarified, and the essential question concerning why FPs are fluorescent has remained unanswered. It is noteworthy that the synthesized model compounds of GFP chromophore do not emit fluorescence. It indicates that the interaction between the chromophore and the surrounding amino acid residues is essential for fluorescence. However, it remains unclear which interactions with which amino acids are important.
  We focused on yellow fluorescent protein (YFP), which is one of the most-used fluorescent proteins. Changing just one amino acid out of the 239 amino acids makes eYFP almost non-fluorescent. We use time-resolved fluorescence spectroscopy to determine the fluorescence lifetime (a measure of fluorescence ability) of fluorescent proteins and elucidate why a single amino acid makes eYFP non-fluorescent, leading to clarify "why are fluorescent proteins fluorescent?".

• An association of fluorescent proteins changes  the fluorescence mechanism.
  When fluorescent proteins are associated in cells, there is a risk that the biological phenomena we observe may be altered. Although it is very important to know the association properties of fluorescent proteins, it has yet to be well understood. We have shown by time-resolved fluorescence anisotropy measurements that the fluorescence mechanism of eYFP is altered by association. We also found that eYFP and the green fluorescent protein (eGFP) differ in their ease of association. eYFP and eGFP differ in only five of their 239 amino acids. By understanding what these five amino acids do and identifying the similarities and differences between eYFP and other fluorescent proteins, we aim to achieve a unified understanding of fluorescent protein association.

• "Diverse Fluorescence Resonance Energy Transfer Processes Originating from the Conformational Heterogeneity of the Calcium Indicator Yellow Cameleon YC3.60"
  Hiroki Tsubota, Yuna Kinoshita, Mamoru Shigeno, and Haruko Hosoi*
  J. Phys. Chem. B 127, 3839–3850 (2023).

• "Three Simultaneous Fluorescence Resonance Energy Transfer Processes and Structural Relaxation of Enhanced Yellow Fluorescent Protein Observed by Picosecond Time-Resolved Fluorescence Anisotropy"
  Hiroki Tsubota, Aimi Takayama, Yuri Takeda, Natsumi Yamada, and Haruko Hosoi*
  J. Phys. Chem. B 125, 7997-8009 (2021).

• "Excited-State Proton Transfer Dynamics in LSSmOrange Studied by Time-Resolved Impulsive Stimulated Raman Spectroscopy"
  Pardeep Kumar, Eduard Fron, Haruko Hosoi, Hikaru Kuramochi, Satoshi Takeuchi, Hideaki Mizuno, and Tahei Tahara*
  J. Phys. Chem. Lett. 12, 7466–7473 (2021).

• "Role of Coherent Low-Frequency Motion in Excited-State Proton Transfer of Green Fluorescent Protein Studied by Time-Resolved Impulsive Stimulated Raman Spectroscopy",
  Tomotsumi Fujisawa, Hikaru Kuramochi, Haruko Hosoi, Satoshi Takeuchi, Tahei Tahara*
  Journal of the American Chemical Society, 138, 3942-3945 (2016). 

• “Solvent Dependence of Two-photon Absorption Spectra of the Enhanced Green Fluorescent Protein (eGFP) Chromophore”
  Haruko Hosoi,* Ryo Tayama, Satoshi Takeuchi, Tahei Tahara
  Chemical Physics Letters, 630, 32–36 (2015). 

• “Smaller 145th Residue Makes Fluorescent Protein Non-Fluorescent: Fluorescence Lifetimes of Enhanced Yellow Fluorescent Protein (eYFP) Y145 Mutants and H148 Mutants”
  Haruko Hosoi,* Sakiko Hazama, Yuri Takeda
  Chemical Physics Letters, 618, 186–191 (2015). 

• “Physisorption Gives Narrower Orientational Distribution than Chemisorption on a Glass Surface: A Polarization-Sensitive Linear and Nonlinear Optical Study”,
  Shoichi Yamaguchi, Haruko Hosoi, Megumi Yamashita, Pratik Sen, Tahei Tahara*
  The Journal of Physical Chemistry Letters, 1, 2662-2665 (2010).

• “Ab initio molecular orbital study of dinitrobenzene radical anions”
  Megumi Kayanuma, Haruko Hosoi, Akiko Furuya, Yuichi Masuda, Keiko Takano*
  Chemical Physics Letters,  494, 139-143 (2010). 

• “Picosecond time-resolved fluorescence study of poly vinyl methyl ether aqueous solution”
  Tsutomu Sakamaki, Tatsuya Fujino,* Haruko Hosoi, Tahei Tahara, Takashi Korenaga
  Chemical Physics Letters,  468 (4-6),171-175 (2009).

• “Direct observation of time-dependent photoluminescence spectral shift in CdS nanoparticles synthesized in polymer solutions”,
  Debabrata Mandal,* Haruko Hosoi, Uma Chatterjee, and Tahei Tahara
  The Journal of Chemical Physics, 130, 034902 (2009).

• “Solvation structure of polyacrylamide fine particle surfaces studied by picosecond time-resolved fluorescence spectroscopy”
  Tsutomu Sakamaki, Tatsuya Fujino,* Haruko Hosoi, Tahei Tahara, and Takashi Korenaga
  Chemistry Letters, 37, 980-981 (2008).

• “Hidden electronic state of enhanced green fluorescence protein”
  Haruko Hosoi, Shoichi Yamaguchi, Hideaki Mizuno, Atsushi Miyawaki, Tahei Tahara*
  Journal of Physical Chemistry B, 112, 2761-2763 (2008).

• “Femtosecond/picosecond time-resolved fluorescence study of hydrophilic polymer fine particles”
  Daisuke Nanjo, Haruko Hosoi, Tatsuya Fujino,* Tahei Tahara, Takashi Korenaga
  Journal of Physical Chemistry B, 111, 2759-2764 (2007).

• “The excited-state structure and the dynamics of 1,3,5-tris(phenylethynyl)benzene as studied by Raman and time-resolved fluorescence spectroscopy”
  Tomonori Nomoto, Haruko Hosoi, Tatsuya Fujino, Tahei Tahara, Hiro-o Hamaguchi*
  Journal of Physical Chemistry A, 111, 2907-2912 (2007).

• "Competition between energy and proton transfer in ultrafast excited-state dynamics of an oligomeric fluorescent protein red Kaede”
  Haruko Hosoi, Hideaki Mizuno, Atsushi Miyawaki, Tahei Tahara*
  Journal of Physical Chemistry B, 110, 22853-22860 (2006).

• “Concatenation of CFP and YFP for efficient resonance energy transfer”
  Satoshi Shimozono, Haruko Hosoi, Hideaki Mizuno, Takashi Fukano, Tahei Tahara, Atsushi Miyawaki*
  Biochemistry, 45, 6267-6271 (2006).

• “Solvent and counter ion effects on intramolecular electron transfer rates of an organic mixed-valence compound”
  Haruko Hosoi and Yuichi Masuda*
  Journal of Molecular Liquids, 119, 89-96 (2005). 

• “Host to guest energy transfer in a self-assembled supra- molecular nanocage observed by picosecond fluorescence quenching”
  Haruko Hosoi, Shoichi Yamaguchi, and Tahei Tahara*
  Chemistry Letters, 34, 618-619 (2005).

• “Solution structure of a tmRNA-binding protein, SmpB, from Thermus thermophilus”
  Tatsuhiko Someya, Nobukazu Nameki, Haruko Hosoi, Sakura Suzuki, Hideki Hatanaka, Michiko Fujii, Takaho Terada, Mikako Shirouzu, Yorinao Inoue, Takehiko Shibata, Seiki Kuramitsu, Shigeyuki Yokoyama, Gota Kawai*
  FEBS Letters, 535, 94-100 (2003). 

• “ESR study on intramolecular electron transfer rate of l,3-dinitrobenzene radical anion in solution”
  Haruko Hosoi and Yuichi Masuda*
  Journal of Molecular Liquids, 90, 279-286 (2001).

• “Solvent effect on rotational motion of perchlorate ion”
  Haruko Hosoi and Yuichi Masuda*
  Journal of Physical Chemistry B, 102, 2995-3002 (1998).

• “Solvent effect on intramolecular electron transfer rate of 1,3-dinitrobenzene radical anion”
  Haruko Hosoi, Yukie Mori, and Yuichi Masuda*
  Chemistry Letters, 27, 177-178 (1998).

• 9th International Discussion Meeting on Relaxation in Complex Systems Aug. 2023
  ”Fluorescence Resonance Energy Transfer Processes and Conformational Heterogeneity in Fluorescent Proteins"
  Haruko Hosoi

• The National Symposium on Radiation and Photochemistry, Kanpur, India Mar. 2015
  “Smaller 145th Residue Makes Fluorescent Protein Non-Fluorescent: Fluorescence Lifetimes of Enhanced Yellow Fluorescent Protein (eYFP) Y145 Mutants and H148 Mutants”
  Haruko Hosoi

• 7th Asian Conference on Ultrafast Phenomena, Busan, Korea Feb. 2012
  “Emission Mechanism of Fluorescent Proteins studied by Advanced Laser Spectroscopy”
  Haruko Hosoi 

• Symposium “Molecular Ensemble 2009”, RIKEN 2009
  “Emission Mechanism of Fluorescent Proteins Studied by Advanced Laser Spectroscopy”
  Haruko Hosoi

• Lecture at University of East Anglia, Norwich, UK 2009
  “Fluorescence Mechanism of GFP:　Electronic States and Dynamics”
  Haruko Hosoi

Professional Experiences

• April 2015-present
  Associate Professor: Department of Biomolecular Science, Faculty of Science, Toho University

• April 2008-March 2015
  Lecturer: Department of Biomolecular Science, Faculty of Science, Toho University

• April 2002-March 2008
  Postdoctoral Research Fellow: Tahara group, Molecular Spectroscopy Laboratory, RIKEN

• April 1999-March 2002
  Research Associate: Ochanomizu University

• April 2001-March 2002
  Visiting Scientist: Genomic Sciences Center, RIKEN

Education

• Ph. D., Ochanomizu University (1998).